Sensors measure data. However, the measurement of the data by the sensor may be affected by time-varying factors. It may therefore be desirable to calibrate the interpretation of measured data so that it can be correctly interpreted.
As an example, a magnetometer measures magnetic field. This may, for example, be used as a compass in a mobile electronic device. The magnetometer may have a fixed relationship to the co-ordinate frame of the mobile device. Measuring the earth's magnetic field relates the magnetometer to the co-ordinate system of the earth. It is then possible to relate the co-ordinate system of the mobile device to the co-ordinate system of the earth, giving a heading for the mobile device.
However, the magnetic field measured by the mobile device can be influenced by factors that are independent of the orientation of the mobile device such as, for example, the presence of a ferro-magnetic material.
It is therefore generally accepted that for magnetometer sensor calibration it is best practise to perform measurements at the magnetometer when the mobile device has a number of different orientations.
It is, however, inconvenient to require a user to perform a pre-determined gesture that orientates the device while acquiring the necessary measurement data for calibration.